feat(markdown): copy button and clipboard routing

- Copy button was missing from code blocks in the preview panel;
  users had no way to grab code without manual selection.
- Clipboard actions (cut/copy/paste/select-all) always routed to the
  Scintilla editor even when focus was in another widget (e.g. the
  preview or a dialog), causing silent no-ops or wrong-target edits.
- <span style> tags in highlighted code broke QTextBrowser's block
  background detection used by the copy button heuristic; <font color>
  is the subset QTextDocument actually parses for inline color.
- Code font family was not applied to <pre>/<code> blocks, only to
  body text, so monospace font preference was ignored in previews.

Author: nullmastermind

src/MarkdownPreviewWidget.cpp

@@ -6,8 +6,16 @@
 #include <QImage>
 #include <QScrollBar>
 #include <QTextDocument>
+#include <QTextBlock>
+#include <QTextBlockFormat>
+#include <QAbstractTextDocumentLayout>
+#include <QTextFrame>
 #include <QtConcurrent>
 #include <QKeyEvent>
+#include <QMouseEvent>
+#include <QToolButton>
+#include <QGuiApplication>
+#include <QClipboard>
 
 MarkdownPreviewWidget::MarkdownPreviewWidget(NotepadNextApplication *app, QWidget *parent)
     : PreviewContentWidget(parent)
@@ -20,8 +28,21 @@ MarkdownPreviewWidget::MarkdownPreviewWidget(NotepadNextApplication *app, QWidge
     m_browser->setOpenExternalLinks(true);
     m_browser->setFrameShape(QFrame::NoFrame);
     m_browser->setReadOnly(true);
+    m_browser->viewport()->setMouseTracking(true);
+    m_browser->viewport()->installEventFilter(this);
     layout->addWidget(m_browser);
 
+    m_copyBtn = new QToolButton(m_browser->viewport());
+    m_copyBtn->setText(QStringLiteral("Copy"));
+    m_copyBtn->setAutoRaise(true);
+    m_copyBtn->setCursor(Qt::PointingHandCursor);
+    m_copyBtn->setStyleSheet(QStringLiteral(
+        "QToolButton { background: palette(mid); border: none; padding: 2px 6px;"
+        " border-radius: 3px; font-size: 11px; }"
+        "QToolButton:hover { background: palette(dark); }"));
+    m_copyBtn->hide();
+    connect(m_copyBtn, &QToolButton::clicked, this, &MarkdownPreviewWidget::copyCurrentCodeBlock);
+
     m_relayoutTimer.setSingleShot(true);
     m_relayoutTimer.setInterval(100);
     connect(&m_relayoutTimer, &QTimer::timeout, this, [this]() {
@@ -122,6 +143,8 @@ void MarkdownPreviewWidget::renderAsync(const QString &text)
 void MarkdownPreviewWidget::applyHtml(const QString &html)
 {
     m_cachedHtml = html;
+    m_copyBtn->hide();
+    m_hoveredCodeBlock = QTextBlock();
     int scrollPos = m_browser->verticalScrollBar()->value();
     m_browser->setHtml(html);
     m_browser->verticalScrollBar()->setValue(scrollPos);
@@ -132,3 +155,86 @@ void MarkdownPreviewWidget::onFontChanged()
     if (m_cachedHtml.isEmpty()) return;
     renderAsync(m_lastSourceText);
 }
+
+bool MarkdownPreviewWidget::eventFilter(QObject *watched, QEvent *event)
+{
+    if (watched == m_browser->viewport()) {
+        if (event->type() == QEvent::MouseMove) {
+            auto *me = static_cast<QMouseEvent *>(event);
+            updateCopyButtonPosition(me->pos());
+        } else if (event->type() == QEvent::Leave) {
+            if (!m_copyBtn->underMouse())  {
+                m_copyBtn->hide();
+                m_hoveredCodeBlock = QTextBlock();
+            }
+        }
+    }
+    return PreviewContentWidget::eventFilter(watched, event);
+}
+
+void MarkdownPreviewWidget::updateCopyButtonPosition(const QPoint &mousePos)
+{
+    QTextCursor cursor = m_browser->cursorForPosition(mousePos);
+    QTextBlock block = cursor.block();
+
+    if (!block.isValid() || !isCodeBlock(block)) {
+        m_copyBtn->hide();
+        m_hoveredCodeBlock = QTextBlock();
+        return;
+    }
+
+    // Find the first block of this code group
+    QTextBlock first = block;
+    while (first.previous().isValid() && isCodeBlock(first.previous()))
+        first = first.previous();
+
+    if (m_hoveredCodeBlock == first && m_copyBtn->isVisible())
+        return;
+
+    m_hoveredCodeBlock = first;
+
+    QRectF firstRect = m_browser->document()->documentLayout()->blockBoundingRect(first);
+    int scrollY = m_browser->verticalScrollBar()->value();
+
+    QSize btnSize = m_copyBtn->sizeHint();
+    int x = m_browser->viewport()->width() - btnSize.width() - 8;
+    int y = static_cast<int>(firstRect.top()) - scrollY + 4;
+
+    if (y < 0) y = 4;
+
+    m_copyBtn->move(x, y);
+    m_copyBtn->show();
+    m_copyBtn->raise();
+}
+
+void MarkdownPreviewWidget::copyCurrentCodeBlock()
+{
+    if (!m_hoveredCodeBlock.isValid()) return;
+    QString text = extractCodeBlockText(m_hoveredCodeBlock);
+    if (!text.isEmpty())
+        QGuiApplication::clipboard()->setText(text);
+}
+
+QString MarkdownPreviewWidget::extractCodeBlockText(const QTextBlock &block) const
+{
+    QString result;
+    QTextBlock b = block;
+    while (b.isValid() && isCodeBlock(b)) {
+        if (!result.isEmpty()) result += QLatin1Char('\n');
+        result += b.text();
+        b = b.next();
+    }
+    return result;
+}
+
+bool MarkdownPreviewWidget::isCodeBlock(const QTextBlock &block) const
+{
+    if (!block.isValid()) return false;
+    QTextBlockFormat fmt = block.blockFormat();
+    // QTextBrowser renders <pre> blocks with a non-default background from our CSS
+    QBrush bg = fmt.background();
+    if (bg.style() == Qt::NoBrush) return false;
+    // Check that the background differs from the document's default (body) background
+    QColor docBg = m_browser->document()->rootFrame()->frameFormat().background().color();
+    return bg.color() != docBg && bg.color().isValid();
+}

src/MarkdownPreviewWidget.h

@@ -5,13 +5,15 @@
 #include "MarkdownRenderer.h"
 
 #include <QTextBrowser>
+#include <QTextBlock>
 #include <QFutureWatcher>
 #include <QHash>
 #include <QUrl>
 #include <QTimer>
 #include <atomic>
 
 class NotepadNextApplication;
+class QToolButton;
 
 class MarkdownPreviewWidget : public PreviewContentWidget
 {
@@ -28,14 +30,23 @@ class MarkdownPreviewWidget : public PreviewContentWidget
 
     void scrollToLine(int line);
 
+protected:
+    bool eventFilter(QObject *watched, QEvent *event) override;
+
 private:
     void renderAsync(const QString &text);
     void applyHtml(const QString &html);
     MarkdownRenderRequest buildRequest(const QString &text);
     void onFontChanged();
+    void updateCopyButtonPosition(const QPoint &mousePos);
+    void copyCurrentCodeBlock();
+    QString extractCodeBlockText(const QTextBlock &block) const;
+    bool isCodeBlock(const QTextBlock &block) const;
 
     NotepadNextApplication *m_app;
     QTextBrowser *m_browser;
+    QToolButton *m_copyBtn = nullptr;
+    QTextBlock m_hoveredCodeBlock;
     QString m_title;
     QString m_basePath;
     QPalette m_palette;

src/MarkdownRenderer.cpp

@@ -266,10 +266,10 @@ QString MarkdownRenderer::highlightCodeBlock(const QByteArray &code, const QStri
     for (int i = 0; i < code.size(); ++i) {
         int s = static_cast<unsigned char>(styles[i]);
         if (s != prevStyle) {
-            if (prevStyle >= 0) html += QStringLiteral("</span>");
+            if (prevStyle >= 0) html += QStringLiteral("</font>");
             SemanticStyle sem = classifyStyle(s);
             const QString &color = colorForSemantic(sem, isDark);
-            html += QStringLiteral("<span style=\"color:") + color + QStringLiteral("\">");
+            html += QStringLiteral("<font color=\"") + color + QStringLiteral("\">");
             prevStyle = s;
         }
         char ch = code[i];
@@ -281,7 +281,7 @@ QString MarkdownRenderer::highlightCodeBlock(const QByteArray &code, const QStri
         default:  html += QLatin1Char(ch); break;
         }
     }
-    if (prevStyle >= 0) html += QStringLiteral("</span>");
+    if (prevStyle >= 0) html += QStringLiteral("</font>");
     html += QStringLiteral("</code></pre>");
     return html;
 }
@@ -305,21 +305,29 @@ QString MarkdownRenderer::buildStyleBlock(const QPalette &palette, bool isDark,
     if (fontSize > 0)
         fontCss += QStringLiteral("font-size:%1pt;").arg(fontSize);
 
+    QString codeFontCss;
+    if (!fontFamily.isEmpty())
+        codeFontCss += QStringLiteral("font-family:'%1',monospace;").arg(fontFamily);
+    else
+        codeFontCss += QStringLiteral("font-family:monospace;");
+    if (fontSize > 0)
+        codeFontCss += QStringLiteral("font-size:%1pt;").arg(fontSize);
+
     return QStringLiteral(
         "<style>"
         "body{background:%1;color:%2;%6padding:16px;line-height:1.6;}"
         "a{color:%3;}"
-        "code{background:%4;padding:2px 4px;border-radius:3px;font-family:monospace;}"
-        "pre{background:%4;padding:12px;border-radius:4px;overflow-x:auto;}"
-        "pre code{background:none;padding:0;}"
+        "code{background:%4;padding:2px 4px;border-radius:3px;%7line-height:normal;}"
+        "pre{background:%4;padding:0.8em 1em;border-radius:4px;overflow-x:auto;line-height:normal;}"
+        "pre code{background:none;padding:0;line-height:normal;}"
         "blockquote{border-left:3px solid %5;padding-left:12px;margin-left:0;}"
         "table{border-collapse:collapse;}"
         "th,td{border:1px solid %5;padding:6px 12px;}"
         "th{background:%4;}"
         "hr{border:none;border-top:1px solid %5;}"
         "img{max-width:100%%;}"
         "</style>"
-    ).arg(bg, fg, link, altBase, mid, fontCss);
+    ).arg(bg, fg, link, altBase, mid, fontCss, codeFontCss);
 }
 
 namespace {

src/dialogs/MainWindow.cpp

@@ -123,10 +123,12 @@
 #include "CrashHandler.h"
 #include "ProfileScope.h"
 
+#include <QApplication>
 #include <QEvent>
 #include <QActionEvent>
 #include <QFont>
 #include <QMenu>
+#include <QMetaObject>
 #include <QPointer>
 #include "DockWidget.h"
 
@@ -197,6 +199,24 @@ class ActionAddedFilter : public QObject
     }
 };
 
+bool isEditorFocused()
+{
+    QWidget *w = QApplication::focusWidget();
+    while (w) {
+        if (qobject_cast<ScintillaNext *>(w))
+            return true;
+        w = w->parentWidget();
+    }
+    return false;
+}
+
+bool forwardClipboardToFocusWidget(const char *slot)
+{
+    QWidget *w = QApplication::focusWidget();
+    if (!w) return false;
+    return QMetaObject::invokeMethod(w, slot);
+}
+
 } // namespace
 
 
@@ -489,11 +509,23 @@ MainWindow::MainWindow(NotepadNextApplication *app) :
 
     connect(ui->actionUndo, &QAction::triggered, this, [=]() { currentEditor()->undo(); });
     connect(ui->actionRedo, &QAction::triggered, this, [=]() { currentEditor()->redo(); });
-    connect(ui->actionCut, &QAction::triggered, this, [=]() { currentEditor()->cutAllowLine(); });
-    connect(ui->actionCopy, &QAction::triggered, this, [=]() { currentEditor()->copyAllowLine(); });
+    connect(ui->actionCut, &QAction::triggered, this, [=]() {
+        if (!isEditorFocused() && forwardClipboardToFocusWidget("cut")) return;
+        currentEditor()->cutAllowLine();
+    });
+    connect(ui->actionCopy, &QAction::triggered, this, [=]() {
+        if (!isEditorFocused() && forwardClipboardToFocusWidget("copy")) return;
+        currentEditor()->copyAllowLine();
+    });
     connect(ui->actionDelete, &QAction::triggered, this, [=]() { currentEditor()->clear(); });
-    connect(ui->actionPaste, &QAction::triggered, this, [=]() { currentEditor()->paste(); });
-    connect(ui->actionSelectAll, &QAction::triggered, this, [=]() { currentEditor()->selectAll(); });
+    connect(ui->actionPaste, &QAction::triggered, this, [=]() {
+        if (!isEditorFocused() && forwardClipboardToFocusWidget("paste")) return;
+        currentEditor()->paste();
+    });
+    connect(ui->actionSelectAll, &QAction::triggered, this, [=]() {
+        if (!isEditorFocused() && forwardClipboardToFocusWidget("selectAll")) return;
+        currentEditor()->selectAll();
+    });
     connect(ui->actionSelectNext, &QAction::triggered, this, [=]() {
         ScintillaNext *editor = currentEditor();
 

tests/test_markdown_renderer.cpp

@@ -144,7 +144,7 @@ private slots:
         MarkdownRenderRequest req = makeRequest("```cpp\nint main() { return 0; }\n```");
         req.resolvedLexers.insert("cpp", "cpp");
         auto result = MarkdownRenderer::render(req);
-        QVERIFY(result.html.contains("<span style=\"color:"));
+        QVERIFY(result.html.contains("<font color=\""));
     }
 
     void highlightedCodeBlock_unknownLanguage_noSpans()